1. Field of the Invention
The present invention relates to a hydrophilic member, more particularly to a hydrophilic member provided with a surface layer excellent in durability and hydrophilicity and a hydrophilic graft polymer to be employed by the hydrophilic member. The invention also relates to a support for a planographic printing plate, particularly to a support for a planographic printing plate having a surface made highly hydrophilic and capable of forming an image with a high image quality.
2. Description of the Related Art
Resin films have been used for a variety of purposes and their surfaces generally show hydrophobicity. Also, regarding inorganic materials such as glass, metals and the like, those showing high hydrophilicity are few.
When the surface of a substrate employing such as a resin film, an inorganic material, or the like, is made hydrophilic, water droplets adhering to the surface are evenly spread on the substrate surface and form a uniform water film, so that fogging of glass, lens, and mirrors can be efficiently prevented and accordingly it is useful to prevent devitrification due to moisture and to assure a visible field at the time of rainy weather. Further, city soot and dust, combustion products such as carbon black and the like contained in an exhaust gas of automobiles and the like, and hydrophobic pollutants such as fats and oils, sealant eluting components and the like hardly adhere to the hydrophilic surface and even if these materials adhere thereto, they can be easily washed off by rainfall and washing water and therefore, it is effective to make the surface hydrophilic for a variety of purposes.
A conventionally proposed surface treatment method for making the surface hydrophilic, for example, an etching treatment, a plasma treatment and the like, can made the surface highly hydrophilic, however the effect is temporary and the hydrophilic state cannot be kept for a long period of time.
A surface-hydrophilic coating using a hydrophilic polymer as one hydrophilic resins has also been proposed (Newspaper, “Kagaku Kogyo Nippo”, Jan. 30, 1995). According to the report, although the coating has hydrophilicity to a certain degree, it cannot be said that the affinity with the substrate is sufficient and accordingly, further high durability is required.
Further, as another film with excellent surface hydrophilicity, a film using titanium oxide has been well-known conventionally. For example, in PCT/JP96/00733, it is disclosed that when a photolysis catalyst-containing layer is formed on the surface of a substrate, the surface is made highly hydrophilic depending on the photo-excitation of the photolysis catalyst and it is reported that if this technique is applied to a variety of composites such as glass, lens, mirrors, external materials, and members dealing with water, the composites are provided with excellent anti-fogging and anti-staining capability. However, such a hydrophilic film using titanium oxide does not have a sufficient film strength and consequently a hydrophilic material having higher wear resistance has been required.
Planographic printing is a printing method utilizing a plate material having an oleophilic region for receiving an ink and an ink-repelling region (a hydrophilic region) which does not receive an ink and receives dampening water. Recently, a photosensitive planographic printing plate precursor (PS plate) has been widely employed.
As the PS plate, those containing a support comprising, for example, an aluminum plate and a photosensitive layer formed thereon, have been realized and are widely used. Using such a PS plate, printing is carried out by removing the photosensitive layer in non-image areas by imagewise exposure and development and utilizing the hydrophilicity of the substrate surface and the oleophilicity of the photosensitive layer in the image areas. In order to prevent stains in the non-image areas of this plate material, high hydrophilicity is required for the substrate surface.
Conventionally, as a hydrophilic substrate to be employed for the planographic printing plate or a hydrophilic layer, an anodized aluminum substrate is used or silicate treatment of the anodized aluminum substrate is further carried out in order to improve the hydrophilicity. Further, investigations of a hydrophilic substrate using such an aluminum support or a hydrophilic layer have been enthusiastically performed and, for example, Japanese Patent Application Laid-Open (JP-A) No. 7-1853 discloses a technique using a substrate treated with an undercoating agent of a polyvinylphosphonic acid and JP-A No. 59-101651 discloses a technique using a polymer having a sulfonic group as an undercoating layer of a photosensitive layer and in other examples, techniques using polyvinylbenzoic acid and the like for undercoating agents have been proposed.
Further, regarding a photosensitive layer used when a flexible support of such as PET (polyethylene phthalate), cellulose acetate and the like is used without using a metal support of such as aluminum, the following various techniques have been proposed: a dampened hydrophilic layer composed of a hydrophilic polymer and a hydrophobic polymer and described in JP-A No. 8-292558, a PET support having a microporous hydrophilic cross-linking silicate surface and described in EP 0,709,228, a hydrophilic layer containing a hydrophilic polymer and cured with hydrolyzed tetraalkyl orthosilicate and described in JP-A Nos. 8-272087 and 8-507727, and the like.
These hydrophilic layers have improved hydrophilicity as compared with a conventional layer to provide a planographic printing plate capable of providing printings which are free of stains at the time of starting printing, however they still have a problem that they peel off after repeated printing and hydrophilicity is decreased over time. Accordingly, it is required to obtain a support for planographic printing plate whose hydrophilic layer does not separate from the support and keeps surface hydrophilicity well without deterioration and which is capable of providing a large number of printings without stains even under severe printing conditions. Presently, further hydrophilicity improvement is also required in terms of practical application.